NDLI: Hot spots in cold adaptation: Localized increases in conformational flexibility in lactate dehydrogenase A4 orthologs of Antarctic notothenioid fishes

Content Provider	PubMed Central
Author	Fields, Peter A. Somero, George N.
Copyright Year	1998
Abstract	To elucidate mechanisms of enzymatic adaptation to extreme cold, we determined kinetic properties, thermal stabilities, and deduced amino acid sequences of lactate dehydrogenase A4 (A4-LDH) from nine Antarctic (−1.86 to 1°C) and three South American (4 to 10°C) notothenioid teleosts. Higher Michaelis–Menten constants (K m) and catalytic rate constants (k cat) distinguish orthologs of Antarctic from those of South American species, but no relationship exists between adaptation temperature and the rate at which activity is lost because of heat denaturation. In all species, active site residues are conserved fully, and differences in k cat and K m are caused by substitutions elsewhere in the molecule. Within geographic groups, identical kinetic properties are generated by different substitutions. By combining our data with A4-LDH sequences for other vertebrates and information on roles played by localized conformational changes in setting k cat, we conclude that notothenioid A4-LDHs have adapted to cold temperatures by increases in flexibility in small areas of the molecule that affect the mobility of adjacent active-site structures. Using these findings, we propose a model that explains linked temperature-adaptive variation in K m and k cat. Changes in sequence that increase flexibility of regions of the enzyme involved in catalytic conformational changes may reduce energy (enthalpy) barriers to these rate-governing shifts in conformation and, thereby, increase k cat. However, at a common temperature of measurement, the higher configurational entropy of a cold-adapted enzyme may foster conformations that bind ligands poorly, leading to high K m values relative to warm-adapted orthologs.
Starting Page	11476
File Format	PDF
ISSN	10916490
e-ISSN	10916490
Journal	Proceedings of the National Academy of Sciences of the United States of America
Issue Number	19
Volume Number	95
Language	English
Publisher	The National Academy of Sciences
Publisher Date	1998-09-15
Access Restriction	Open
Rights Holder	The National Academy of Sciences
Subject Keyword	Research in Higher Education
Content Type	Text
Resource Type	Article
Subject	Multidisciplinary

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